1. Technical Field
Embodiments of the present disclosure relate generally to analog to digital converters, and more specifically to a non-binary successive approximation analog to digital converter.
2. Related Art
Successive approximation analog to digital converters (SA-ADC, also referred to as successive approximation register (SAR) ADC) are often used to generate digital codes representing corresponding samples of an analog signal received as input. SA-ADCs employ the successive approximation principle (SAP) for generation of the digital codes. Approximations of the analog signal are generated, and compared with the analog signal till the digital codes representing the approximations have been resolved to the accuracy of number of bits available in the SA-ADC for representing a sample of the analog signal.
In a binary SA-ADC, the successive approximations are generated in a binary-weighted fashion. Thus, for example, the first approximation may equal half the full-scale range of the SA-ADC, with the following (successive) approximations reducing geometrically by a factor of two (i.e., ¼, ⅛, 1/16, etc) till the least significant bit (LSB) is resolved. Correspondingly, binary SA-ADCs may be said to employ a binary search algorithm, the radix (base) used in the binary search being two.
A non-binary SA-ADC employs a non-binary search to resolve some or all bits of the digital value representing a sample of the analog signal. Thus, the search ranges for successive approximations may reduce geometrically by a factor other than two. For example, the first approximation may equal half the full-scale range of the SA-ADC. But the following (successive) approximations reduce geometrically by a factor of N (N not equal to 2), i.e., 1/N, 1/N2, 1/N3, etc.
One prior SA-ADC uses a non-binary weighted digital to analog converter (DAC). A non-binary weighted DAC employs circuit elements (such as capacitors or resistors that are controlled to generate approximations of an analog signal sought to be converted to digital form) that have magnitudes related in a non-binary-weighted fashion. In another prior SA-ADC, the DAC is designed as a thermometric DAC. In general, design of a DAC implemented to employ non-binary weighted elements, i.e., a non-binary weighted DAC, may pose difficulties in the layout stage of implementation of the SA-ADC. Further, the use of a thermometric DAC may require complex logic and layout routing for performing the non-binary search.